Electric power providers that supply electric power have conventionally adjusted the electric power supplied to an electric distribution system by power generators that are capable of freely adjusting output power (adjustable power sources) according to variations in the anticipated power demand (amount of power consumption) and have thus achieved balance between supply and demand of power in the electric power distribution system. Thermal power plants, which are capable of adjusting output power at relatively high speed, are chiefly used as the adjustable power-source equipment.
Large-scale generators that include adjustable power sources typically require a certain amount of lead time from the state of halted operation until being capable of supplying electric power (in the order of at least 30 minutes). Thus, in order to deal with fluctuations in the demand for power, the above-described adjustable power source must be activated before the demand for electric power becomes great. When the anticipated range of fluctuation in the demand for power is particularly great, the amount of generated power by hydroelectric power plants or nuclear power plants, in which the output power cannot be freely adjusted (only to the extent that output power can be turned ON and OFF), must be decreased and a plurality of adjustable power sources must be activated. Normally, adjustable power sources such as thermal power plants are frequently operated at a low utilization rate, whereby increasing generation efficiency is problematic. As a result, the cost of power generation inevitably increases with increase in the adjustable power sources that are in operation.
Recent years have seen a demand for a major diffusion and expansion of renewable power sources such as photovoltaic generation (hereinbelow abbreviated as PV) and wind power generation (Wind Farms, hereinbelow abbreviated as “WF”) that can reduce the release of warming gases during operation and that are directed toward realizing a sustainable society. However, the output of renewable power sources changes according to the weather. In other words, renewable power sources entail the problem of instability as regards the amount of power that can be generated.
Renewable power sources such as PV and WF are power generators in which the output power cannot be freely adjusted, and linking these renewable power sources to a power distribution system gives rise to further variations that cannot be controlled in the supplied power in addition to the above-described variations in the demand for electric power. This leads to an even greater need for adjustable power sources to cope not only with variation in the demand for power but with variations in supplied power as well. This leads to further increases in the costs of power generation for electric power providers and, when consumers that own renewable power sources sell back surplus power to a power provider, is a factor for setting a low price for the electric power that is sold.
In addition, in a electrical power distribution system that is linked to many renewable power sources, the possibility exists that even if adjustable power sources operate at a low utilization rate, the output power of the adjustable power sources and the generated electric power of renewable power sources may surpass the power demand, whereby the balance between supply and demand of electric power cannot be achieved, which can lead to instability of power frequency and power outages.
Still further, because consumers are increasingly able to choose electric power providers in recent years due to increased liberalization of the electric power market, adjustable power sources have also become necessary for absorbing the consequent differences in demand for electric power and the supplied electric power. Normally, the electric power that is supplied to a consumer is managed by the system operator (electric power provider) that manages the system to which the consumer is connected. Accordingly, when the consumer selects a power provider, the electric power provider that has contracted with the consumer does not necessarily coincide with the system operator that operates the system to which the consumer is connected. On the other hand, because power for the consumer is distributed by way of the system to which the consumer is connected (electric power forwarding), when the amount of power generated by the electric power provider with whom the consumer is contracted does not match the amount of power consumed by the consumer (power demand), the difference must be absorbed by the system to which the consumer is connected. In other words, the difference between the amount of generated power and the amount of demand increases in the electric power distribution system in which most electric power is used by forwarding electric power to another electric power provider, and adjustable power sources are again necessary for absorbing this difference. In order to resolve disparities in electric power adjustment between the electric power provider with whom the consumer is contracted and the system operator, a payment setup is currently adopted by which the amount of power generated by the electric power provider with whom the consumer is contracted and the amount of electric power consumed by the consumer (power demand) are each measured and recorded for every predetermined interval (for example, 30 minutes), and the consumer or the electric power provider with whom the consumer is contracted pays penalties to the system operator that manages the electric power distribution system of the consumer according to the differences between supply and demand.
As an example of a method of reducing unbalance in supply and demand of electric power in this type of electric power distribution system that is linked to renewable power sources, Non-Patent Document 1 proposes a method in which the amount of generated power by PV is estimated based on the estimated amount of solar radiation, and the amount of electric power that is to be supplied to the electric power distribution system (reverse power flow) based on the estimated amount of generated power is reported to the electric power provider in advance. Non-Patent Document 1 further proposes that the difference between the estimated amount of PV-generated power and the actual amount of generated power be absorbed by the charge and discharge of a storage device.
If the amount of power that is to be supplied to a electric power distribution system is in this way reported to the electric power provider in advance, the electric power provider is able to establish or amend the operating plans of, for example, a generator, based on the estimated amount of generated power of each PV. Alternatively, if the amount of power that is to be supplied to the electric power distribution system is reported to the consumer, the consumer is able to adjust the amount of power consumption based on the estimated amount of generated power of PV. As a result, balance in the supply and demand of electric power of the electric power distribution system can be achieved. In addition, reverse power flow refers to the supply of electric power that is generated by a renewable power source owned by the consumer to a power distribution substation of the electric power provider from the consumer.
As described hereinabove, Non-Patent Document 1 proposes the use of a PV for which the amount of generated power can be relatively easily estimated as a renewable power source, and further, the absorption of the difference between the estimated amount of generated power of the PV and the actual amount of generated power by the charge and discharge of a storage device. However, even a method of this type cannot avoid error between the amount of electric power that is reported to the electric power provider or consumer in advance and the amount of electric power that can actually be supplied to the electric power distribution system. In particular, when WF is used as the renewable power source, fluctuation in the amount of generated power due to weather conditions is great, whereby the amount of generated power is difficult to accurately predict.
Accordingly, balance between supply and demand of electrical power is difficult to achieve when error between the estimated amount of generated power that is reported to the electric power provider or consumer and the amount of power that can actually be supplied to the electric power distribution system is great and the amount of the linked renewable power sources to the electric power distribution system becomes great. In addition, when a multiplicity of adjustable power sources are prepared with consideration given to error between the estimated amount of power that is reported and the amount of electric power that is actually supplied to the electric power distribution system, the cost of power generation inevitably increases.